Drilling rig arrangement

ABSTRACT

The invention provides a system for operating a drilling rig on a drilling vessel, the system comprising a drilling tower ( 2 ) having at least two segments ( 4, 5 ), a first segment ( 4 ) is fixedly connected to the drilling vessel ( 1 ), a second segment ( 5 ) is connected to the first segment ( 4 ), said second segment ( 5 ) is adapted to move longitudinally relative the first segment ( 4 ) by raising and lowering means. A tool ( 8 ) is suspended from at least one wire ( 16 ), said at least one wire ( 16 ) is extending over at least one sheave ( 7   a,    7   b ) on top of the second segment ( 5 ), said at least one wire ( 16 ) is coupled to with a passive compensator arrangement ( 20 ) and a winch ( 14 ), said passive compensator ( 20 ) is connected to the winch ( 14 ).

FIELD OF THE INVENTION

The present invention relates to an arrangement for a drilling rig thatserves as supporting tower structure for lifting and supporting drillingmachines and other tools. More particularly the invention relates to aretractable drilling rig with a passive heave compensation system andwinch system arranged in connection with the drilling rig.

BACKGROUND OF THE INVENTION AND PRIOR ART

Drilling ships and semi-submersible platforms are equipped with drillingrigs to support the necessary lifting of equipment under variousoffshore operations. Usually, these derricks are equipped with passiveand active compensator systems to compensate for relative movementsbetween the vessel and the seabed due to vessel wave impact.

The wave compensation systems are designed for handling of maximum loadsat the seabed or down hole. This is often overcome by installing apassive compensator in the top of the drilling rig. This passivecompensator compensates the weight hanging on the crown block relativethe movement between the vessel and the seabed by means of a cylindersystem of a pre-charged accumulator. Other systems are compensated byactive draw-works/winches without any passive/autonomous compensatorsystems.

The traditional draw-work systems lifts also only one single part wireled through many discs to achieve the correct ratio between the crownblock and the lift block. This could result in challenges related tosecurity, the lifetime of the cable and noises due to the high speed ofthe cable and in the winch system.

The passive compensation systems in the top of drilling rig is heavy andnot easily accessible for maintenance. Considerable weight in the top ofthe derrick is detrimental to the properties of the vessel. They alsohave large cylinder area adapted to the need to compensate passively formaximum load at ultra deep water operations. This large cylinder areasresults in large load variations at small loads at shallower waters andeasier well intervention operations. In case of activedraw-work-configuration the rig have no back-up in case of possible lossof electrical power supply and is therefore less suitable for criticaloperations.

The drilling rigs (derricks) consists traditionally of a pyramidal steelframework with square or rectangular cross-section assembled together toa fixed structure. The drilling rigs have a complex structure. Theycomprises multiple parts that may lead to high risk of falling objects.The height of the rigs are fixed without any possibilities to change theheight when the drilling rigs are mounted together. This makes themaintenance work on top of the drilling rig more difficult.

Ice formation on the framework of the drilling rigs is another challengeof drilling rigs according to prior art. This is especially a problemwhen operating in arctic environments.

SUMMARY OF THE INVENTION

The invention provides a system for operating a drilling rig on adrilling vessel. The system is distinctive in that the system comprisinga drilling tower having at least two segments, a first segment isfixedly connected to the drilling vessel, a second segment is connectedto the first segment, said second segment is adapted to movelongitudinally relative the first segment by raising and lowering means,a tool is suspended from at least one wire, said at least one wire isextending over at least one sheave on top of the second segment, said atleast one wire is coupled to with a passive compensator arrangement anda winch, said passive compensator is connected to the winch.

Preferable embodiments of the system are defined in the dependent claims2-12.

The invention also provides a heave compensation arrangement adapted topassively compensate a drilling tool suspended on at least one wireextending over at least one sheave on the top of a drilling tower. Theheave compensation system is distinctive in that the compensationarrangement comprising at least one compensation sheave wherein said atleast one wire is extending over said sheave and to said winch, adampening device is arranged operatively between the at least onecompensator sheave and the winch, said dampening device having aplurality of compensator cylinders adapted to compensate differentloads.

Preferable embodiments of the heave compensation arrangement is definedin in the dependent claims 14-16.

The invention also provides a winch system. The winch system isdistinctive in that the system having plurality of hydraulic motorsadapted to be selectively engaged with a common winch drum.

Preferable embodiments of the winch system are defined in the dependentclaims 18-20.

The present invention relates to a development of a cost and energyefficient concept for drilling and intervention tower with accompanyingelevator/draw-work system that is flexible with a focus on increasedsecurity and is easier in terms of fabrication, installation andmaintenance. Central to this technology development is more suitabilityfor operations in arctic waters and it is also more adaptable todifferent types and sizes of the vessel or the platform. The conceptincludes a cylindrical tower-/mast construction with wire sheaves at thetop to support a balanced lifting of the travelling assembly. The toweris telescopic ie it could be lowered and raised and has a flangedfastening point towards the drilling floor structure. The tower/mastcomprising at least two segments that allows the upper segment of thetower to be lifted and lowered in the lower segment by means of typicalinternal toothed rod drives to reduce the building and sailing height.At the top of the drilling rig, there are mounted lifting sheaves wherethe lifting wires are guided above.

Lifting and compensating for the top drive or drilling tool and landingof pipe segments to the seabed is carried out by means of acombined/integrated winch and a heave compensator located at or possiblybelow the drill floor level. The system typically includes a winch withone wire drum operating typically 6 separate lifting wires connected tothe same drive shaft, each of these wires is led through typically 2:1gear compensation system as an integrated part of the hoistingapparatus. Hence a combined unit for lift and active- and autonomouspassive heave compensation is achieved. The winch system could haveseveral digital driving units which allows optimal transmission andpossibilities for active heave compensation. The typically 6 cylindricalcompensators (jiggerwinch) are connected to a controllable pre-chargedvolume of gas which contributes to an almost constant balanced load in aheave motion relatively restricted by the wave motion and associated bythe stroke length of the cylinders. To achieve the best compensationperformance, of this minimum load variation, with small loads in thewires could one or more of the compensation cylinders be unloaded,either hydraulically and/or mechanically (in standby position), so thatthe load is transferred and compensated by the necessary number ofcompensation cylinders which are optimal related to compensation loadand on the other hand optimal to avoid large friction and dynamicallyload variations.

The present invention is considered to have the following advantagesover prior art:

-   -   Optimized hydraulic drive and heave compensation system that        reduces power requirements and hence lower greenhouse gas        emissions.    -   Reduced height of the vessel when sailing to increase the        stability of the vessel and obtain less air resistance when the        ship is in transit. Moreover to pass under bridges. This opens        access for instance to the Caspian Sea as well as other        places/waters where reduced sailing height is a critical factor        and also give possible access by rig cranes to all area of tower        and drill floor.    -   Great potential for weight savings because of cylindrical tower        segments used in balanced lifting operation in relation to        traditional framework drilling rig. There are smaller components        thus easier handling of parts.    -   Significantly lower center of gravity that allows larger deck        load and improving sea qualities on the drilling vessel.    -   A low pipe setback results in a lower center of gravity and the        possibility of the ship of making transit with a full setback.    -   Open drilling floor area provides significantly easier lifting        and handling of pipes and other equipment on the rig floor area.        It also gives the cranes full access to the entire rig floor.        This feature gives also excellent overview over all operations.    -   Less complex tower structure that increases the safety by        greatly reducing the risk of falling objects.    -   Modular design that simplifies installation on board the vessel        and reduces the risk of errors during installation.    -   By utilizing the production of wind turbine mast will provide        major savings and potential for production efficiency compared        to classic drills with derrick/drawworks and top compensation        arrangement.    -   Flexible drill concept that automatically adapts operations for        all depths without influencing compensation characteristics    -   The drilling rig arrangement have larger operation window. The        wind area of the tower structure is reduced.    -   Icing of structures can be prevented by easily heating of the        inside of mast/tower. Surface area and therefore the heating        area of the tower is reduced compared with a traditional        derrick. This is an improvement since ice can accumulate on        traditional frame work tower and cause hazardous falling object.    -   Multiple lifting wires provides high redundancy and safety. This        is a great improvement versus traditional draw-work systems        where the crown block is suspended by only one single wire,        hence the significant reduction in the risk of falling objects        on the drill floor.    -   The drilling structure can be retracted thus reduce the height        allows access by deck cranes at the top of the tower that leads        to easier maintenance and increased uptime of the overall        drilling system. A wider range of shipbuilding locations could        also be utilized. Could also use shipyards with smaller crane        capacity and less available shipyards obstructed by bridges.    -   The passive compensator is redundant with multiple cylinders to        compensate the heave motion of the vessel.    -   Winch and compensator system can cooperate to achieve the        optimally activated areas adapted to the winch load and the        requirements of the compensator capacity.    -   The lifting winch uses multiple hydraulic motor winches which        give an excellent resolution.    -   There are excellent access for maintenance of all main        components located at rig floor level.

The main objective of the present invention is to provide a drillingrig, which drilling rig is beneficial over the previous technology withrespect to issues mentioned.

FIGURES

The invention will now be explained in detail with reference to theaccompanying drawings, in which:

FIG. 1 shows a drilling rig arrangement according to the presentinvention with retractable drilling towers mounted on a drilling vessel.

FIG. 2 shows the drilling tower arrangement schematically in an elevatedposition, viewed from the side.

FIG. 3 shows the drilling tower arrangement schematically in a retractedposition, viewed from the side,

FIG. 4a-4j shows a possible means for raising and lowering the drillingrig tower in detail.

FIGS. 4a-4b and 5a-5g shows the guiderails attached to the towersegments in detail.

FIG. 5h-5i shows the first segment of the driling tower and theguiderails attached to the first segment.

FIG. 6 is an overview of the drilling rig arrangement with the winch andheave compensation system according to the present invention. The winchand compensation system does not have the actual position relative tothe drilling rig tower.

FIG. 7a shows the winch and compensator and winch system schematically,viewed from the side.

FIG. 7b shows the winch and compensator and winch system schematically,viewed from the behind.

FIG. 8a-8c shows the passive heave compensation system with differentcompensator capacity.

FIG. 9a-9c is an isometric view of the heave compensation system in FIG.8a -8 c.

FIG. 10a-10b is an isometric view of passive compensator system attachedto the winch system and a detail view of the winch system.

DETAILED DESCRIPTION

FIG. 1 shows a drilling rig arrangement mounted on a drilling vessel 1.The Figure shows two equal retractable drilling towers 2 connected to arig floor 3 on the vessel 1. The drilling rig towers 2 are arranged,next to one another on the vessel 1. The drilling rig towers 2 are shownin an elevated position in the figure and comprising a first, lowersegment 4 and a second, upper segment 5. The second segment 5 isretractable within the first segment 4. A possible embodiment of theinvention is a drilling rig tower 2 with more than two segmentscomprising a base segment, one or more middle segments and an uppersegments. The middle and the upper segments are retractable. Well center9 are arranged beside each of the towers 2. The towers 2 are mounted tothe rig floor outside of the well center 9. A top drive 8 or main blockare arranged in a vertical line above the well center 9, suspended froma at least one wire 16, and is adapted to be in operational connectionwith the well center 9. Pipe/riser segments 11 are arranged on pipeshouts 12 in a distance outside of the rig floor. The pipe segments aremoved towards the well center 9. The top drives 8 are lifting the pipesegments 11 vertically and positioning the pipe segments 8 verticallyabove the well center 9 and into the well (not shown). The pipe segments11 are also stored below in a riser setback storage area 13 arrangedbelow the rig floor 3. Drill pipe stands are located in the setbackstorage area 13 where the stands are transferred to the pipe shout 12 bya pipe handling equipment 18. The pipe shout 12 presents the stand tothe topdrive 8. The topdrive 8 brings the stand in to the wellcenter 9.

A passive compensator 20 (shown in FIG. 2) and a winch system 14 arearranged at or near the rig floor level 3 beside each of the drillingrig tower 2. The winch system 14 with the passive compensator system 20and the well center 9 are arranged on the opposite side of the drillingrig tower 2. On the top of the drilling rig tower 2 there are arrangedat least one first sheave 7 a and at least one second sheave 7 b. Thefirst sheave 7 a is arranged at the side of the tower 2 in facing thewell center 9, the second sheave 7 b is arranged at the side of thetower 2 facing the winch 14. The sheaves 7 a, 7 b are arranged with thecenteraxis on shafts 15 a, 15 b. The shafts 7 a, 7 b are connected tothe top of the tower 2 through a support arrangement 27 arranged on bothends of the shafts 15 a, 15 b. The shafts 15 a, 15 b are substantiallyparallel. Preferably there are arranged several first sheaves 7 a onshaft 15 a and several second sheaves 7 b on shaft 15 b, forming twoclusters of sheaves at the top of the drilling tower 2. (This is seen indetail in FIG. 4b ). A possible embodiment of the invention is toarrange one large sheave or one cluster of sheaves at the top of thedrilling rig tower 2.

The top drive 8 is elevated and lowered into position using the winchsystem 14. The top drive 8 is in one end connected to wires 16. Thewires 16 is extending over the sheaves 7 a, 7 b on top of the secondsegment 5. The wires 16 are extending further along the side of thedrilling rig tower 2 facing the winch 14 and are extending below thepassive compensator 20 (FIG. 2) before the wires are connected to thewinch 14 at the end of the wire 16. There could be arranged one wire 16between the winch system 14 and the top drive 8, but preferably thereare arranged several parallel wires 16, each wire extending over onefirst sheave 7 a and one second sheave 7 b at the top of the drillingrig tower 2, and one compensator sheave 21 (FIG. 2) at the bottom of thecompensation arrangement 20. This is shown in detail in FIG. 2.

The figure shows the drilling tower 2 arranged on the drilling vessel 1,but the arrangement could also be mounted on other drilling facilitiessuitable for the invention.

FIG. 2 shows the drilling rig arrangement schematically, the drillingrig arrangement are viewed from the side and the drilling tower 2 is inan elevated position. A socket 24 arranged at the lower part of thefirst segment 4 is bolted to a mounting in the rig floor 3. The secondsegment 5 and the first segment 4 is in this position connected to eachother through a flange connection 6. This flange connection 6 is fixingthe segments 4, 5 to each other when the drilling rig tower 2 is in theelevated position. This position is also the working position of thedrilling rig.

It is not possible to retract the tower before the flanged connection 6between in the first segment 4 and the second segment 5 are released.

The winch system 14 and the passive compensator system 20 are arrangedon the opposite side of the top drive 8 as described in FIG. 1. Thewinch system 14 is attached to the drilling deck 3. The passivecompensation system 20 is normally arranged at the underside of thewinch system 14 but the system could also be arranged in the samehorizontal plane as the winch system. Or other arrangements relative tothe winch system is also possible. The passive compensation system 20 isnormally arranged below the drilling deck 3, but the compensation systemcould also be arranged above the rig floor, this being an embodiment ofthe invention. The passive compensation system 20 comprises acompensator sheave 21 or a cluster of parallel sheaves arranged on ashaft 28 and means for passive compensation 25. These passivecompensation means 25 are arranged between the winch 14 and thecompensator sheaves 21.

A frame structure 26 is arranged on two sides of the passivecompensation system 20, the frame structure is extending from theunderside of the winch system 14 and the drilling deck 3. The framestructures 26 provides support to the compensation system 20. Incorrespondence with the system there is also arranged an activecompensation system 29 (shown in FIG. 6).

FIG. 3 shows the drilling rig arrangement schematically viewed from theside in a retracted position. This position is suitable for maintenanceor transportation, but not as a working position for drilling the well.In this position the second segment 5 is disconnected from the flangedconnection 6 and the second segment 5 is retractable within the firstsegment 4.

The following FIGS. 4a-4f shows the raising and lowering mechanism ofthe drilling tower in detail.

FIG. 4a shows the drilling tower 2 schematically, viewed from the side.FIG. 4b shows a cross section view of the drilling tower 2, seen fromthe line k-k in FIG. 4a . At the top of the second segment 5, thesheaves 7 a are shown. The sheaves 7 a are situated beside each other onthe same shaft 15 a as described earlier. The second sheave 7 b aresimilar to sheaves 7 a.

Means for raising and lowering of the retractable tower 39 are shown inFIG. 4b-4i . A pitch rack 40 is arranged in the center of the firstsegment 4, extending from the rig floor 3 to or near the end of thefirst segment 4. The rack 40 having teeth 41 adapted to engage circulargears 42. The gears 42 are arranged on both sides of the rack 40. Thegears 42 are arranged on a vertical plate 44. The plate 44 is arrangedon one side of the pitch rack 40 with several gears 42 arranged in pair.The pair of gears are situated on opposite sides of the pitch rack 40.The gears 42 are adapted engage with the teeth 41 of the pitch rack 40and move the second segment 5 in the vertical direction. This is shownin detail in FIGS. 4d, 4e, 4g and 4 h.

FIG. 4b-4e shows three pair of gears 42 arranged on a vertical line oneach side of the pitch rack 40, but this does not limit the invention.There could be arranged more than three or less than three pair of gears42 if that is suitable in relation to the present invention. There couldalso be more than one vertically aligned plate 44 arranged within thedrilling rig tower 2.

The plate 44 is attached to an inner guide structure 43. The inner guidestructure 43 is a cylindrical segment with a diameter slightly less thanthe lower segment 4. It has guide rollers 45 arranged around peripheryof the inner guide structure 43 near both ends of the inner guidestructure 43. The guide roller 45 rest against the inside of the lowersegment 4 and is adapted to move in the vertical direction along thelower segment 4 by the gear 42 and pitch rack 40 arrangement. An upperpart 46 of the inner guide structure 43 is connected to the bottom partof the upper segment 5 with bolts or similar connecting means so thatthe upper segment 5 moves the same distance in the vertical direction asthe inner guide structure 43 is moved within the lower segment 4.

Other arrangement for raising or lowering the second segment 5 is alsopossible. Other typical possibilities for raising and lowering the towersegment are by use of a winch arrangement and/or by lowering the uppersegment 5 into the lower segment column 4 with a large external crane.

FIG. 4a-4b also shows guiderails 30, 32 for guiding the second segmentsin when it is retracted. The second segment 5 having a pair of upperguiderails 30 attached to the outside of the second segment 5. At thefirst segment 4, a pair of lower guiderails or guide tubes 53 or areattached to the outside of the first segment 4. The guidetubes 53 areoriented at the same side as the upper guiderails 30. In the Figure, theguiderails 30 and guidetubes 53 are oriented at the side facing the topdrive 8, but any orientation suitable for the invention are possible.The guiderails 30 and guidetubes 53 are attached to the tower 2 throughfastening means or brackets 31, 33. The upper brackets 31 are arrangedat a suitable distance from each other along the upper guiderails 30,and the lower brackets 33 are arranged at a suitable distance from eachother along the guidetubes 53.

At the inside of the second segment 5 there are arranged fixationdevices 35. These fixation devices 35 corresponds to and are adapted tobe connected to bracket segments 51 of the brackets 31. When thedrilling rig tower 2 is in the elevated position, the fixation devices35 are connected to the bracket segments 51. The fixation devices 35 arereleased from the bracket segments 51 before the lowering of the secondsegment 5 into the first segment 4 and the upper guiderails 30 could bemoved a distance away from the upper segment 5 and a distance from theother guiderail 30. An opposite bracket segment 50 is connected to theguiderail 30. This is further described in FIG. 5a -5 g.

FIG. 5a-5d shows the guide rails described in FIG. 4a-4b in detail. FIG.5a shows the drilling tower 2 viewed from the front. There two parallelguide rails 30 extending along the upper segment 5 and the two parallelguide rails 32 extending along the lower segment 4. The FIG. 5a showsthe position where the bracket segments 51 are released from thefixation devices 35 (FIG. 4b ). The brackets 31 are in this position notconnected in sleeve point the guide rails 30 could then move out andthen away from each other and away from the second segment 5.

FIG. 5b shows a sectional view of the transition between the uppersegment 5 and the lower segment 4. Guide pins 52 are attached to thebrackets 31 and arranged between the pair of guiderails 30. The guidepins 52 are align vertically with guide tubes 53 which are attached tothe lower guide rails 32. The in guide tubes 53 having each alongitudinal groove (not shown). The guide pins 52 are adapted to beguided down in the guide tubes 53 when the upper segment 5 of the tower2 is retracted.

There are also shown gripping means 56 for handling pipe segments 11.

FIG. 5c shows an isometric view of the upper guiderails 30 with brackets31 and FIG. 5d shows a sectional view of one of the brackets 31. FIG. 5gshows the guiderails from FIG. 5c , frontview and sideview.

FIG. 5e shows a sectional view of the fixation devices 35 at the insideof the upper guide rail 30 and FIG. 5f shows a cross view of thefixation devices at the line H-H. The fixation device 35 is locking thebracket segment 51 with an internal bolt 54 that passes through anopening 55 in the bracket segments 51.

FIGS. 5h and 5i shows isometric views of the first segment 4 with theguide tubes 53 shown in detail.

FIG. 6 shows the drilling rig arrangement schematically, viewed from theside. The figure shows a detailed overview of the winch system 14, thepassive compensation system 20 and an active compensation system 29according to the present invention. The systems 14, 20 and 29 are notarranged in actual position related to each other or the drilling tower2 in this figure.

The winch system 14 comprises a plurality of winch motors 60 connectedto a hydraulic power system 61 and accumulators 72. The hydraulic winchmotors 60 are digital and utilize a multiple digital hydraulic motors 60providing excellent resolution and optimized power consumption. Thisprovides accurate positions to the load to be lifted or lowered by thewinch system 14. When there is a heavy load on the hook or top drive 8,most of the hydraulic motors 60 or motor segments are online and themotor power required to the winch 14 is high. In the other case whenthere is no load on the top drive 8 or hook only a few of the hydraulicmotors or motor segments 60 are online, most of the motors or motorsegments 60 are idling. The hydraulic power from the power unit 61 thatis not needed in the system could then be led to the accumulator 72until it's needed again for heavy loads or high speed operation of thewinch 14. This system enables to equalize the power need from thegenerator during a sequence of the tripping inn/lifting operation togive a more optimized generator performance for a typical sequenceddrilling operation. That's again gives less peak power needed from thegenerator sets and by this also improves the overall greenhouse gasemissions for this operation. During lowering of a load the returnedpower from the winch motors 60 are directly transferred back to theaccumulator 72 from the braking energy. This for use during the nextlifting operation or for equalizing the power regeneration back to theship/rig system during a long trip inn/lowering sequence where there isa lot of fluctuating excess power generated back to the ship/rig powermanagement system. The accumulators 72 are operatively coupled to thewinch system 14 to boost and store the hydraulic flow and pressure whenhigh power is needed or generated back from the system. The storedenergy in the accumulators 72 is also possible to use for emergency liftoff operation with the winch system 14 during a black ship scenario. Thewinch motors 60 could also be of other types than hydraulic for instanceelectrical motors as a direct drive system or in combination with anelectrical power storage and management system

The passive compensation system 20 is connected to the winch system 14and comprises a cylinder 62 and a cylinder housing 63 which areconnected to an oil/gas separator 64 and pressure vessels 65 forcompensating the cylinder 62 position relative the movement of thedrilling vessel 1 in order to maintain the position of the top drive 8in a steady position.

The wires 16 are extending from the top drive 8 and runs over the uppersheave cluster. The wires 16 are further extending to the compensatorsheave cluster 21 and runs via the compensator sheave cluster to thewinch 14. This gives a 2:1 exchange on the compensator cylindermovement.

This system achieves a combined unit for hoisting winch and active andautonomous passive compensation. The winch system 14 comprises severaldigital drives that allows optimal transmission of power and possibilityfor passive and active wave compensation.

FIG. 7a shows the winch and compensation system in detail, viewed fromthe side.

FIG. 7b shows the winch and compensation arrangement seen in FIG. 4, inviewed from the behind. There are several compensator sheaves 21arranged beside each other and also several wires 16 arranged besideeach other extending round parts of the periphery of the compensatorsheaves 21. There are arranged six passive cylinders 62 a, 62 b, 62 cbetween the winch 14 and the compensator sheaves 21.

FIGS. 8a, 8b and 8c shows different configuration of the passivecompensation arrangement 20. In FIG. 8a all of the six cylinders 62 a,62 b, 62 c are online and compensating the load. In this position themaximum compensator capacity is obtain. This system is often used inloads in a range between 655-1000 sh. Ton but are not limited to thatrange.

In FIG. 8b there are four cylinders 62 a, 62 c online. The last twocylinders 62 b are released from a compensator sheave holder 66 arrangedbetween the compensator sheaves 21 and the cylinders 62 a, 62 b, 62 cinto the cylinder housing 63 and will not give any compensation to thesystem in this position.

This position is most suitably for loads in a range between 335-655 sh.Ton, but the use are not limited to this range.

In FIG. 8c there are only two cylinders 62 c online and the other fourcylinders 62 a, 62 b are retracted into a corresponding cylinder housing63. This position provides the minimum compensator capacity and aresuitable for small loads, typically between 0-35 sh. ton but not limitedto the range. The cylinders 62 c on the outside are normally connectedto a compensator sheave frame 58 arranged between the compensatorsheaves 21 and the cylinder 62 c, the cylinders 62 c could also bereleased from the compensator sheave frame 58 like the other cylinders62 b, 62 a.

The cylinders 62 a, 62 b, 62 c are adapted to abut or be connected tothe compensator sheave frame 58 when they are online. If one of the pairof cylinders are broken, the other pair of cylinders could be set onlineinstead.

The variable number of heave cylinders 62 a, 62 b, 62 c ensures optimalheave compensation characteristics/performance at any drilling or downhole operation eliminating unnecessary dead weight and friction losses.The cylinders 62 a, 62 b, 62 c operate in pair to balance thecompensation in arrangement 21.

FIGS. 9a, 9b and 9c shows an isometric view of the passive compensationsystem from 8 a, 8 b and 8 c.

FIGS. 10a and 10b shows an isometric view of the winch system andpassive compensation system as shown in FIGS. 7a and 7 b.

The winch system comprises a plurality of hydraulic motors 60 which areadapted to engage with a common winch drum 71. The plurality ofhydraulic motors are engaged in a circle at one end of the winch drum71. A circle of hydraulic motors 60 are arranged at each end of thewinch drum 71. The number of motors online depends on the load on hookor top drive 8. When for instance an empty top drive 8 or hook islowered a few of the motors are online, the rest of the motors areidling.

I the opposite case, when the top drive 8 or hook are hoisted withweight on the hook, a few of the motors are idling, the rest of themotors are online.

1. A system for operating a drilling rig on a drilling vesselcharacterized in that the system comprising a drilling tower (2) havingat least two segments (4, 5), a first segment (4) is fixedly connectedto the drilling vessel (1), a second segment (5) is connected to thefirst segment (4), said second segment (5) is adapted to movelongitudinally relative the first segment (4) by raising and loweringmeans, a tool (8) is suspended from at least one wire (16), said atleast one wire (16) is extending over at least one sheave (7 a, 7 b) ontop of the in second segment (5), said at least one wire (16) is coupledto with a passive compensator arrangement (20) and a winch (14), saidpassive compensator (20) is connected to the winch (14).
 2. A systemaccording to claim 1, wherein the drilling floor (9) is arranged on theoutside of the drilling tower (2), said tool (8) is vertically alignedabove the well center (9).
 3. A system according to claim 1 or 2,wherein the passive compensator arrangement (20) comprises a pluralityof cylinders (62 a, 62 b, 62 c), arranged between the winch 14 and aleast one compensator sheave (21), the at least one wires (14) extendingvia the at least one compensator sheave (21) to the winch (14).
 4. Asystem arrangement according to claim 3, wherein the plurality ofcylinders (62 a, 62 b, 62 c) are arranged parallel to each other, saidplurality of cylinders (62 a, 62 b, 62 c) are operable in pairs.
 5. Asystem according to claim 3 or 4, wherein some of the cylinders (62 a,62 b, 62 c) can be coupled and discoupled selectively from a compensatorsheave frame (58).
 6. A system arrangement according to any one of claim1-5, wherein the compensation arrangement (20) having three pair ofcylinders (62 a, 62 b, 62 c) an outer pair of cylinders (62 c) arefixedly connected between the at least one compensator sheave (21) andthe winch (14), an inner pair of cylinders (62 a) and a middle pair ofcylinders (62 b) are in releasable connection with the at least onecompensator sheave (21), said outer pair of cylinders (62 c) arearranged on the outside of the middle pair of cylinders (62 b) and theinner pair of cylinders (62 a).
 7. A system arrangement according to anyone of claim 1-6, wherein the winch system (14) having digital hydraulicmotors.
 8. A system according to claim any one of claims 1-7, whereinthe raising and lowering means comprising a pitch rack (40) arrangedwithin the lower segment (4), said pitch rack (40) having teeth (41)adapted to engage circular gears (42), said gears (42) are arranged onan inner guide structure (43), said inner guide structure (43) isarranged within the first segment (4) and is fixedly connected to thebottom of the second segment (5), said guide structure (43) is adaptedto move along the inner surface of the first segment (4).
 9. A systemaccording to any one of claim 1-8, wherein the segments (4, 5) of thedrilling tower (2) are modular, cylindrical segments (4, 5).
 10. Asystem according to any one of claim 1-9, wherein the first second (4)and second segment (5) are bolted together in an elevated position ofthe drilling rig tower (2).
 11. A system according to any one of claim1-10, wherein at least one upper guiderail (30) is releasably connectedto the second segment (5).
 12. A system according to any one of claim1-11, wherein a third segment are arranged between the first segment (4)and second segment (5).
 13. A heave compensation arrangement adapted topassively compensate a drilling tool (8) suspended on at least one wire(16) extending over at least one sheave (7 a, 7 b) on the top of adrilling tower (2) characterized in that the compensation arrangement(20) comprising at least one compensation sheave (21) wherein said atleast one wire (16) is extending over said sheave (21) and to said winch(14), a dampening device (20) is arranged operatively between the atleast one compensator sheave (21) and the winch (14), said dampeningdevice (20) having a plurality of compensator cylinders (62 a, 62 b, 62c)) adapted to compensate different loads
 14. A heave compensationarrangement according to claim 13, wherein some of the compensatorcylinders (62 a-62 c) can be coupled and discoupled selectively from acompensator sheave frame (58).
 15. A heave compensation arrangementaccording to any one of claim 13-15, wherein the dampening device (20)comprising three pair of cylinders (62 a, 62 b, 62 c), said first andsecond pair of cylinders (62 a, 62 b) are adapted to retract within thecylinder housing, the plurality of cylinders (62 a, 62 b, 62 c) arearranged parallel to each other, said cylinders (62 a-62 c) are operablein pairs.
 16. A heave compensation arrangement according to any one ofclaim 13-15, wherein the passive compensation system (20) are arrangedbelow the winch (14) and below the rig floor (3).
 17. A winch systemcharacterized in that the winch system having plurality of hydraulicmotors (60) adapted to be selectively engaged with a common winch drum(71).
 18. A winch system according to claim 17, wherein the plurality ofhydraulic motors (60) are arranged in a circle at one end of said drum(71).
 19. A winch system according to claim 17 or 18, wherein a circleof hydraulic motors (60) are arranged at each end of said drum (71). 20.A winch system according to any one of claim 17, 18 or 19, wherein theplurality of hydraulic motors (60) are arranged in a circle at theinside of said drum (71).
 21. A winch system according to any one ofclaim 17, 18 or 19, wherein the plurality of hydraulic motors (60) arearranged in a circle at the outside of said drum (71).
 22. A winchsystem according to any one of claim 17-21, wherein at least oneaccumulator 72 is operatively coupled to boost the hydraulic pressurewhen high power is needed.